This application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2000-086829 filed on Mar. 27, 2000, the entire contents of which are herein incorporated by reference.
1. Field of the Invention
The present invention generally relates to an image processing and forming apparatus such as a painter, a copier, a facsimile, etc., and in particular relates to an image processing and forming apparatus capable of minimizing a dropout in a toner image.
2. Discussion of the Background
As proposed in Japanese Patent Application Laid Open No. 11-127348, a printer that separates an input image signal into character and picture pattern areas and processes image data while giving a priority to resolution in a character area and to gradation in a picture pattern area in order to obtain a high printout reproducibility is well known.
FIG. 23 illustrates such a type of a background printer that includes a scanner xcex3 conversion circuit 101, an image area separation circuit 102, a smoothing filter 103, an edge emphasis filter 104, a printer xcex3 correction circuit 105, a gradation circuit 106, and a write apparatus that employs a laser.
An image signal input through a scanner (not shown) is converted from reflection rate data to brightness data by the scanner y conversion circuit 101. The input image signal is also input to an image area separation circuit 102 and separated into a character area and a picture pattern area. For example, the image area separation circuit 102 outputs an image area separation signal that has one bit which represents a picture pattern area by xe2x80x9c0xe2x80x9d and a character area by xe2x80x9c1xe2x80x9d. The smoothing filter 103 applies weak smoothing to the character area and strong smoothing to the picture pattern area referring to the image separation signal.
Further, the edge emphasis filter 104 emphasizes an edge in the character area and weakens the same in the picture pattern area referring to the image separation signal, thereby emphasizing the edge of the image. The printer y correction circuit 105 raises printer y in the character area and slightly flattens the same in the picture pattern area referring to the image area separation signal, thereby correcting an output value.
The gradation circuit 106 applies a mimetic half tone process such as a dither process, an-error diffusion process, etc., to the picture pattern area referring to the image area separation signal. An output from the gradation circuit 106 is transmitted to the write apparatus 107 via an interface (not shown) thereby controlling a laser device that is provided in the write apparatus 107. Specifically, the output controls activation of a laser beam that is irradiated from the laser device to a photosensitive section member in a pulse state.
As proposed and well known in Japanese Patent Application Laid Open No. 04-248766, an image area separation circuit 102 includes a possible character area detection device that detects a possible character area (i.e., a character edge area) and a white ground area detection device that detects an area neighboring on a white ground. In addition, the image area separation circuit 102 determines an area that belongs to both of the possible character area and the white ground neighboring area as a character area. According to such an image area separation circuit 102, an inside of a character having a relatively bolder line such as a gothic typeface typically is determined as a picture pattern area.
FIG. 24 illustrates one example of brightness data that is obtained by the scanner y conversion circuit 101. Specifically, a brightness change is illustrated along with a scanning direction of an image that has relatively bolder and half tone (about 128/256 gradations) characters and is put on a white ground. In such brightness data, a middle portion of the character, an edge area thereof, and a white ground are determined by the image area separation circuit 102 as a picture pattern area, a character area, and a picture pattern area, respectively.
FIG. 25 is a diagram for illustrating other brightness data, when edge emphasis treatment is applied by the edge emphasis filter 104 in a manner such that an edge portion between a picture pattern area and a character area is selectively emphasized.
Further, FIG. 26 is a diagram for illustrating still other brightness data when a center of a character is determined by the gradation circuit 106 as a picture pattern area and a line dither pattern having (1xc3x972) pixels is applied thereto. As noted therefrom, a signal in the picture pattern area is converted into multiple high frequency pulses.
In addition, FIGS. 27 and 28 are diagrams for illustrating both a shape of a laser spot whose ON/OFF is controlled by a signal (i.e., brightness data) of FIG. 26 and an image that is to be reproduced on a print medium. Specifically, FIG. 27 illustrates a case when a laser ON/OFF operation is controlled per a pixel to align with a left side thereof as a reference. In contrast, FIG. 28 illustrates a case when a laser ON/OFF operation is controlled per a pixel to align with a right aide thereof as a reference. As understood from these drawings, the laser spot 108 is large and a density of the image reproduced on the print medium is high as a level of the brightness data is high. Thus, an image can be reproduced on a print medium in accordance with an input image signal.
However, according to such an image processing method, since a level of brightness data is lowered by edge emphasis as illustrated in FIG. 26, a dropout occasionally appears in an edge portion between a left side character area and a picture pattern area as illustrated in FIG. 27 when a laser ON/OFF is controlled in a left side alignment. In addition, a dropout occasionally appears in an edge portion between a right side character area and a picture pattern area as illustrated in FIG. 28 when a laser ON/OFF is controlled in a right side alignment.
To overcome such drawbacks, Japanese Patent Application Laid Open No. 11-127348 includes a character contour area detection device that detects a contour of a character, a background area detection device that detects an area neighboring on a background, and a character inside a high density area detection device that detects a character inside a high density area whose coloring density level exceeds a prescribed level and an whose adjacent area includes uniformity of a coloring density higher than a prescribed level.
Japanese Patent Application Laid Open No. 11-127348 further includes an image separation device that separates and determines images that a character contour and background area and a character inside high density area are determined as character areas, and a remaining area as a picture pattern area. According to such a technology, a dropout can be minimized because the character inside a high density area is determined as a character area, and accordingly, an inside portion of the character is not separated into the character area and the picture pattern area.
As an edge emphasis filter 104, a Laplace operation edge emphasis filter has widely been known. However, a Laplace operation has disadvantages such as over or under shoot that occurs in a portion other than an edge due to ringing. As a result, an edge generally is excessively emphasized and a dropout appears on a color background or the like, and in particular, when the under shoot occurs, thereby causing remarkable deterioration of an image.
As improvements of such above-described technology, Japanese Patent Application Laid Open Nos. 7-162687 and 8-149305 have been known.
Specifically, Japanese Patent Application Laid Open No. 7-162687 proposes a technology that can remove excessive emphasis that occurs when an edge is emphasized at around an area boundary by controlling an edge emphasis level. Japanese Patent Application Laid Open No. 8-149305 also proposes a technology that can minimize ringing that generally occurs when an edge is emphasized in a prescribed manner by a Laplace operation that is widely employed. Specifically, a value of a target pixel is compared with five values of ambient pixels (e.g., a larger value of the (K) rank, a smaller value of the (L) rank, when a plurality of ambient pixel values is ranked from the largest or smallest, a pair of values obtained by adding a pair of prescribed offsets to these larger and smaller values, and an average of these larger and smaller values). Then, a prescribed output of the edge emphasis is determined among these five comparisons.
However, hardware (i.e., construction) of an image separation device of a printer of Japanese Patent Application Laid Open No. 11-127348 is complex when compared, for example, with that of Japanese Patent Application Laid Open No. 4-248766. This is because the technology of Japanese Patent Application Laid Open No. 11-127348 should be provided with an image separation device that includes a character contour area detection device that detects a contour area of a character, a background area detection device that detects an area that neighbors on a background, a character inside high density area detection device that detests a character inside a high density area whose coloring density level exceeds a prescribed level and an whose adjacent area includes uniformity of a coloring density is higher than a prescribed level, and an area determination device that determines both a character contour and background area and a character inside a high density area as character areas, and a remaining area as a picture pattern area.
In addition, the edge emphasis filter of Japanese Patent Application Laid Open No. 7-162587 proposes only in relation to an area boundary, and is not efficient against excessive emphasis that causes at a sharp edge degree such as a character portion. This indeed can be improved when the proposition of Japanese Patent Application Laid Open No. 8-149305 is employed. However, gradation may be deteriorated depending upon an image because only a value defined from ambient pixels can be output.
Accordingly, an object of the present invention is to address and resolve the above and other problems and provide a new image forming apparatus.
The above and other objects are achieved according to the present invention by providing a novel image data processing apparatus that includes an image area separation signal generating device for generating an image area separation signal. A dither pattern storage device for storing at least one dither pattern and an address decoding device for decoding a prescribed address of the dither pattern storage device in accordance with the input image signal and similar signals may be included. In addition, a changing device for changing a character/picture pattern switch position in the image area separation signal using a signal having a prescribed width and output from a pixel clock counter, and a picture pattern/character selecting device for selecting one of character and picture pattern areas in accordance with the changed image area separation signal may also be included.
In another embodiment, the address decoding device may include a pixel clock counter that has at least one bit and counts a number of pixels in a main scanning direction, a horizontal synchronization signal counter that has at least one bit and counts a number of pixels in a sub scanning direction, and a flip-flop that adjusts delay in an input image signal.
In yet another embodiment, the character/picture pattern switch position changing device may include a flip-flop that latches the input image area separation signal, an inverter that logically inverts the input image area separation signal, and an AND circuit that applies an AND gate to outputs from the flip-flop, and a selector that selects one of signals of the AND circuit and an image separation signal and outputs an image area separation change signal.
In still another embodiment, the image data processing apparatus may include a dither pattern size storage device that stores a number of pixels included in the mimetic halftone pattern, an address decoding device that decodes a prescribed address of the dither pattern storage device in accordance with an input image signal and the number of pixels of the mimetic halftone treatment pattern stored in the dither pattern size storage device, and a changing device that changes the character/picture pattern switch position with reference to an output of the address decoding device.
In another embodiment, the image data processing apparatus may include a write reference position setting device that sets a reference position for writing an input image signal with a dot either to left or right side alignments, and a changing device that changes the character/picture pattern switch position with reference to a signal set in the write reference position setting device and an output of the address decoding device.
In yet another embodiment, an image data processing apparatus may include a value detecting device that detects a value of pixels neighboring on a target pixel, an edge emphasis device that emphasizes an edge of the input image signal using a Laplace operation, a bias adding device that adds a prescribed amount of bias to the value of the neighboring pixels detected by the value detecting device, and a signal outputting device that compares and outputs one of the outputs from the bias adding device and edge emphasis device.
In another embodiment, the value of neighboring pixels is obtained by adding the prescribed amount of bias either to the maximum or minimum values thereof.
In still another embodiment, the bias amount may be determined from the neighboring pixel value.